Black bump on my dog belly

I found this black bump on my dog belly today. It is smooth to the touch but it is a bit raised compared to the skin. I'm not sure for how long this could be here, but he doesn't seem to be bothered by it. Any thoughts on what it can be and on how urgent it can be? Appreciate in advance, I'm a bit preoccupied and I think I will try to schedule an appointment tomorrow.

Hello!  For me this could be days urgent rather than weeks urgent.  It's hard to know how long that mark has been there and hard to know how long a biopsy would take if that was decided upon, so days may well make little difference.  However, if it were to be sinister, then at some point comes the day that makes the difference.  It is important to get the mark checked so that in the event that it were to be sinister, action could be taken sooner rather than later.

Tomorrow seems very reasonable.